New Mexico Spaceport Authority board members voted during a regular meeting Wednesday to extend the runway by another 2,000 feet. Spaceport America is the world's first terminal, hangar and runway built specifically for commercial space travel.

Virgin Galactic, which will be the spaceport's anchor tenant, determined through a battery of test flights and simulations that more room would be needed for landings under certain circumstances.

"It's really being done for safety," spaceport spokesman David Wilson said. "It was a guess until they started dropping it and simulating and doing different scenarios, how this thing was going to behave on the runway. This is all a product of the testing and the characteristics of the vehicle."

Backed by British billionaire Richard Branson, the commercial space line has been developing its craft and rocket engines in California's Mojave Desert. The company plans to begin moving into the hangar and terminal facility later this year, and the runway extension is not expected to cause delays.

The runway was dedicated by Branson and other officials in October 2010 with much fanfare.

Stretching across a flat dusty plain 45 miles north of Las Cruces, the runway is designed to support almost every aircraft in the world, day-to-day space tourism flights and payload launch operations. It is 42 inches thick and includes a 14-inch layer of concrete.

The extension will cost $7 million, Wilson said. Money will be reassigned within the spaceport's $209 million taxpayer-financed budget to absorb the cost of the change.

Designing the extension will take six to eight months.

Virgin Galactic has said rocket testing is continuing and commercial flights are at least a year away.

Wilson said the extension did not come as a surprise to spaceport board members. As part of the agreement Virgin Galactic had with New Mexico to build the spaceport, any technical changes that resulted from development of the spaceship technology would have to be accommodated by the state.

One scenario considered was if the rocket ship's engines did not fire. That would require the craft to glide back to the spaceport, loaded with unburned fuel. That would mean the craft would be heavier and would require more room to land.

Other factors involve New Mexico's altitude and high temperatures, which make the air thinner.

"That dictates longer runways," Wilson said.

Branson and Virgin Galactic officials have said repeatedly that everything possible will be done to ensure safety once commercial flights begin.

Unlike experimental programs run by NASA, Wilson said Spaceport America and Virgin Galactic are based on business models and investments.

"Obviously safety has to be at the highest level, especially when you're talking about commercial passenger service," he said.

Branson announced last week that Virgin Galactic had netted its 500th customer, actor Ashton Kutcher. Others include Hollywood types, international entrepreneurs, scientists and space buffs.

At $200,000 a ticket, the space tourists get a 2 1/2-hour flight with about five minutes of weightlessness and views of Earth that until now only astronauts have been able to experience.